HOLLOW FILAMENT CROSSSECTIONS CONTAINING FOUR CONTINUOUS VOIDS

Abstract: Continuous synthetic filaments having a four sided cross-sectional contour and four substantially equispaced continuous voids are disclosed. The voids have a substantially round or nonround shape, and each void is substantially centered on a side of the filament's contour.

Description: TITLE HOLLOW FILAMENT CROSS-SECTIONS CONTAINING FOUR CONTINUOUS VOIDS BACKGROUND OF THE INVENTION This application is a continuation-in-part of Application Serial No. 08/82,878, filed June 25, 1993, which is a division of Application Serial No. 07/969,323, filed October 30, 1992, which is a division of Application Serial No. 07/735,241, filed July 24, 1991, now U.S. Patent No. 5,190,821. Field of the Invention The present invention relates to continuous synthetic filajnents having a four sided cross-sectional shape containing four continuous voids positioned at distinct locations. The filaments are especially suitable for making carpets which demonstrate improved soiling performance and durability. Description of the Related Art Those skilled in the art have proposed many different ways to improve the "soiling performance" of continuous synthetic filaments. By the term "soiling performance", it is meant the apparent resistance of a textile material to visible soiling which may be independent of the soiling which actually occurs. One effort involves producing filaments having continuous voids extending throughout their lengths. As described by Champaneria et al., United States Patent 3,745,061, it is known to produce filaments having at least three continuous nonround voids. These voids form about 10% to about 35% of the filament volume and are set against the corners of the filament's cross-sectional contour which is substantially free of re-entrant curves. W. Lochelfeld et al., German Patent No. DL 90,840/ '72 teaches a process for spinning filaments having four hollow spaces. These filaments have high stability due to an approximately circular cross-section. However, the circular cross-section also tends to decrease the bulk of these filaments. Although such conventional filaments, as described above, have a somewhat effective soiling performance, there is a need for filaments having even greater soiling performance which also demonstrate high bulk and durability. The filaments of the present invention provide an improved combination of soiling performance, bulk, and durability and are especially suitable for carpets receiving a high amount of traffic. SUMMARY OF THE INVENTION The present invention relates to continuous filaments, comprising a thermoplastic synthetic polymer and characterised by a solid axial core and four substantially equispaced voids, a void content of about 6% to 25%, and a four-sided cross-sectional contour. The voids have a substantially round or nonround shape and each void is substantially centered on a side of the contour. Preferably, the shape of the voids is triangular-like, wherein the apex of each void is directed at the central longitudinal axis of the core, and the base of each void is substantially centered on a side of the contour. The configurations of the voids may be substantially eguidi ensional. Suitable polymers include polyolefins such as polypropylene, polya ides such as nylon 66 and nylon 6, and polyesters such as polyethylene terephthalate. Carpet yarns may be made from the filaments of this invention and tufted into backings to form carpets demonstrating improved soiling performance and low glitter. DESCRIPTION OF THE FIGURES Fig. 1 is a face view of a spinneret capillary for spinning filaments which have voids positioned at the corners of the filament's cross-section. Fig. 1-A is a cross-sectional view taken from photomicrographs of polypropylene filaments spun through capillaries of the type shown in Fig. 1. Fig. 2 is a face view of a spinneret capillary suitable for spinning filaments of this invention. Fig. 2-A is a cross-sectional view taken from photomicrographs of polypropylene filaments spun through capillaries of the type shown in Fig. 2. Fig. 3 is a schematic diagram illustrating a process for producing filaments of this invention. Fig. 4 is a cross-sectional view taken from photomicrographs of nylon 66 filaments spun through capillaries of the type shown in Fig. 2. Fig. 5 is a cross-sectional view taken from photomicrographs of polyester filaments spun through capillaries of the type shown in Fig. 2, wherein the outside diameter of the capillaries is 0.0791 inches. Fig. 6 is a cross-sectional view taken from photomicrographs of polyester filaments spun through capillaries of the type shown in Fig. 2, wherein the outside diameter of the capillaries is 0.0120 inches. Fig. 7 is a face view of a spinneret capillary suitable for spinning filaments of this invention, wherein the sides of the filaments* square contour have small curves. Fig. 7-A is a cross-sectional view taken from a photomicrograph of nylon filaments spun through capillaries of the type shown in Fig. 7. Fig. 8 is a face view of a spinneret capillary suitable for spinning filaments of the prior art, wherein voids are positioned at the corners of the filament's cross-section and the filament's sides are free of curves. Fig. 8-A is a cross-sectional view taken from a photomicrograph of nylon filaments spun through capillaries of the type shown in Fig. 8. Figure 9 is a cross-sectional view taken from a photomicrograph of nylon filaments spun through capillaries of the type shown in Fig. 7. The nylon polymer used to make these filaments had a higher RV than that of the polymer used to make the filaments shown in Fig. 7-A. DETAILED DESCRIPTION OF THE INVENTION The filaments of this invention are generally prepared by spinning molten polymer through spinneret capillaries which are designed to provide the desired configuration of the voids and overall cross-section of the filament. The filaments may be prepared from synthetic, thermoplastic polymers which are melt-spinnable. These polymers include, for example, polyolefins such as polypropylene, polyamides such as nylon 66 and nylon 6, and polyesters such as polyethylene terephthalate. Both copolymers and^melt blends of such polymers are also suitable. Generally, in the melt spinning process, the molten polymer is extruded into air or other gas, or into a suitable liquid, where it is cooled and solidified. Suitable quenching gasses and liquids include, for example, air at room temperature and chilled air. It is recognized that the specific spinning conditions may vary depending upon the polymer used and the desired properties for the filament. For example, the filament's percentage of voids (void content) may normally be increased by increasing the quenching rate and/or the polymer melt viscosity. In this invention, the filaments have a void content of about 6% to 25% and preferably between about 8% to 25%. It was found that soiling performance increases gradually from about 6% to 25% void content with substantially no improvement in soiling performance occurring between about 25% and 35% void content. At a void content higher than about 35%, the filaments are weakened. The polymer spinning dopes may also contain conventional additives, such as antioxidants, dyes, delustering agents, antistatic agents, etc. Referring to Fig. 2, a suitable segmented spinneret capillary for forming the filaments of this invention is illustrated. The four-sided capillary includes four slot units (1), (2), (3), and (4) each comprising of peripheral (5) and radial (6) spokes through which the polymer flows. Between the slots, there are four substantially equispaced segments (7), (8), (9), and (10) , through which none of the polymer flows. These segments define the shape and size of the voids in the resulting filaments. The segments may have various nonround shapes to form corresponding nonround voids in the filaments. Alternatively, the segments may have round shapes to form corresponding round voids in the filaments. Preferably, there are four-, substantially equispaced triangular-like segments. The apex of each triangular-like segment is directed at the central longitudinal axis of the capillary, and the base of each segment is substantially centered on a side of the capillary. A typical capillary has an outside diameter (A) of 0.0791 inches, peripheral spokes (5) having a width (B) of 0.0080 inches, and radial spokes (6) having a width (C) of 0.0065 inches. The spacing (D) between the ends of the radial spokes is typically 0.0100 inches, while the spacing (E) between the ends of the peripheral spokes is 0.0079 inches. The depth of the capillary is 0.035 inches, and the length to diameter (L/D) ratio (0.035/0.0065) is about 5.4. It is understood that the above dimensions may vary, depending upon the melt viscosity and surface tension of the specific polymer. Preferably, the spinneret capillary has the configuration shown in Figure 7 with the dimensions described in the following Example 8. However, it is understood that other spinneret designs may be used to make the filaments of this invention. It is critical that the segments be arranged in order that the four voids of the resulting filaments are oriented away from the corners and aligned with the sides of the filament's cross-sectional contour. The segments are positioned such that each void is substantially centered on a side of the cross-section, as shown in Fig. 2-A. The filaments are further characterized by a solid axial core, and the voids are continuous, substantially equispaced, and preferably equidimensional. It is recognized that filaments having voids in their axial cores would also demonstrate effective soiling performance, although the durability of such filaments may be inferior to filaments having a solid axial core. Furthermore, regardless of void shape, it is believed that maximum soiling performance occurs when the largest dimension of the void is positioned at the sides, near the edges, of the filament. In a preferred configuration, the segments are arranged to for n a filament having triangular-like voids, wherein the apex of each void is directed at the central longitudinal axis of the core, and the base of each void is substantially centered on a side of the filament's cross-sectional contour, as shown in Fig. 2-A. It is also important that the filament's cross- sectional contour be free of substantial convex or concave curves. If the filament's periphery has substantial convex curves, the filament's overall cross-section is substantially circular and bulk is adversely effected. Conversely, if the filament's periphery has substantial concave curves, areas are created which tend to collect soil and reduce soiling performance. However, small convex or concave curves along the filament's cross-sectional contour may be desirable, depending on the intended end-use of the filament. Such curves reduce the glitter or sparkle observed when light strikes the filaments without seriously affecting the bulk or soil hiding performance. Cross-sections of filaments having small curves along their contour are shown in Figures 7-A and 9. The key improvement demonstrated by the filaments of this invention is their greater soiling performance. Furthermore, the filaments have greater durability, while retaining such properties as bulk, luster and carpet covering power. Filaments having small curves on the sides of their cross-sectional contour also exhibit a low glitter, wool-like appearance. The filaments of this invention are especially suitable for producing commercial and residential carpets, particularly level loop pile carpets. The filaments may be used to form yarns which are subjected to texturing and subsequently tufted into a carpet backing material by techniques known in the art. A preferred texturing process involves a hot air jet-bulking method as described in Breen and Lauterbach, United States Patent 3,186,155. TESTING METHODS Percent Void Determination The percent void of the filament's cross-section (void content) was measured using a Du Pont Shape Analyzer, Model VSA-1, which measured the area of the voids and the area of the filament's entire cross-section. The Du Pont Shape Analyzer characterizes textile fiber yarn cross-sections by performing numerical analysis on the digital contour of individual filament cross-sections. A simple calculation of dividing the void area by the cross-section area provides the % void of the filament's cross-section. Carpet Soiling Performance Soiling performance tests of commercial level loop and residential Berber level loop carpets composed of the filaments of this invention were conducted. The tests involved exposing the carpets to a significant amount of soil by an actual foot traffic test. Typical foot traffic levels ranged from 150,000 to 1,000,000, at a rate of about 60,000 to 80,000 traffics per week. The foot traffic was counted by a pressure sensitive pad located under the carpet and attached to an electronic counter. The counter registered traffic when the carpet was stepped on by individuals traveling through a corridor. The dimensions of the carpet samples can vary. The width of the carpet sample is typically about six (6) feet in order to cover the width of the corridor. The length of the carpet is typically in the range of about six (6) to thirty (30) inches, depending upon the available number of samples. In this instance, the commercial level loop carpet measured fifteen (15) inches x six (6) feet, and the residential Berber carpet measured thirty (30) inches by six (6) feet. The carpets were vacuumed on a nightly basis, regardless of the exact amount of foot traffics. On a weekly basis, reflectance measurements were made on the different carpet samples using a Minolta Chroma Meter CR-100 measuring device. The CR-100 is a compact tristimulus color analyzer for measuring reflected subject color. Color readings are taken at five (5) different areas on the carpet sample. The Chroma Meter calculates a ΔE, color difference, for each reading. ΔE color deviation represents total color difference. The equation assumes that color space is Euclides (three-dimensional) and calculates ΔE as the square root of the sum of the squares of the three components representing the difference between coordinates of the sample and the standard, as shown by the equation below: ΔE = [(Δ L*)2 + (Δa*)2 + Δ b*)2]l/2 where L* is a brightness variable, and a* and b* are chromaticity coordinates. When conducting a soiling performance comparison test, it is important to test all of the samples at the same time and try to maintain the same floor location. Walk off mats are also used to prevent carpet samples closest to the corridor entrance from receiving an unduly amount of traffics. This prevents bias in the testing. The carpet samples in this test were solution dyed during the extrusion process. All samples had virtually the same amount of draw finish. The samples were not exposed to any kind of water treatment (dyeing, scouring, etc.) before testing. Filament Cross-Section Model In order to measure the improvement in soiling performance of the filament of this invention, a model was built to represent different filament cross-sections. The objective of this model was to measure soiling performance in a quantitative manner. In order to perform this analysis, the model was constructed using a solid clear plastic square block measuring two (2) inches x two (2) inches. Each half of the solid block was then drilled with four (4) circular holes (voids) to form a block having a cumulative total hole (void) content of 11%. In one half of the block, the holes were drilled in such a manner that each hole was positioned at a corner of the block. This configuration represented conventional filaments, wherein, the voids are aligned with corners of the filament's cross-section. In the remaining half of the block, the holes were drilled in suςh a manner that each hole was aligned with a side of the block. This configuration represented the filaments of this invention, wherein each void is substantially centered on a side of the filament's cross- section. Measurements were then taken at four (4) different viewing angles along the outside surface of the block to determine the soiling performance of each representative cross-section model. The first measurement was on the flat side (reference 0° angle) and then at 15° intervals up to 45°, which was the corner of the cross-section. Any measurements past the 45° point were mirror images of the original 4 points and repeated themselves around the surface. The measurements were recorded as the percentage of soiling performance at each viewing angle. The soiling performance was calculated by measuring the sum of the widths of the bands of visual distortion across the total width of the block and dividing it by the total width of the block. Whereby, the total width of the block changed at each viewing angle, i.e., at 0°, the total width was the actual width of the block (2 inches). At 45°, the total width was the length of the diagonal across the cube's face (2.8 inches). The formula is as follows: Soiling Performance = WD (inches) x 100 WB (inches) where WD is the width of visual distortion and WB is the total width of the block. Relative Viscosity Relative Viscosity (RV) of nylon 66 is the ratio of the absolute viscosity of a solution of 8.4 weight percent nylon 66 (dry weight basis) dissolved in formic acid solution (90% formic acid and 10% water) to the absolute viscosity of the formic acid solution, both absolute viscosities being measured at 25°C. Prior to weighing, the polymer samples are conditioned for two hours in air of 50% relative humidity. Relative Viscosity of polyethylene terephthalate measured in hexafluoroisopropanol (HRV) is the ratio of a solution of 4.J5 weight percent polyethylene terephthalate (dry weight basis) dissolved in hexafluoroisopropanol to the absolute viscosity of hexafluoroisopropanol, both absolute viscosities being measured at 25 * C. Glitter Carpet samples were placed on a table. A 1500±100 Lux light source was suspended 3.5 meters above the table. Samples were observed from an angle between about 27.5- 37.5 degrees from the horizontal plane of the table. A panel of six experts in the field of carpets rated the samples on a scale of 1 (no glitter) to 5 (high glitter) . Ratings reported are the average of the ratings by each of the six experts. The foregoing testing methods were used in the following examples. These examples illustrate the present invention but should not be construed as limiting the scope of the invention. EXAMPLES Example 1 In this Example, polypropylene filaments having different cross-sections were prepared. Sample A Polypropylene filaments having cross-sections, as shown in Fig. 2-A, were made by the following method. A melt-spinning dope containing 10.8% MFI (Melt Flow Index) polypropylene polymer was prepared by melting the polymer at 260°C and cofeeding it with about a 3% light beige color concentrate in a screw extruder. The melt-spinning dope was then spun at 4.1 grams/minute/hole through a spinneret having the configuration shown in Fig. 2. Referring to Fig. 2, the outside diameter (A) of the spinneret capillary was 0.0791 inches. The width (B) of the peripheral spokes (5) was 0.0080 inches, while the width (C) of the radial spokes (6) was 0.0065 inches. The spacing (D) between the ends of the radial spokes was 0.0100 inches, v while the spacing (E) between the ends of the peripheral spokes was 0.0079 inches. The depth of the capillary was 0.035 inches, and the length to diameter (L/D) ratio (0.035/0.0065) was about 5.4. Referring to Fig. 3, the filaments passed from the spinneret (11) into a quenching chimney (12) at a rate of 120 filaments per end, where a cooling gas was blown past the hot filaments (13) at about 1.3 ft./sec. velocity. The filaments were pulled from the spinneret (11) and through the quenching ?one by means of a puller or feed roll (14) , rotating at 815 yards per minute (ypm) . After quenching in air at a temperature of about 15°C, the filaments were treated with aqueous liquid (a mixture of water and non-aqueous draw-finish material) by contacting a finish applicator (15) . Next, the filaments passed across the heated (65°C) feed roll (14) to heated (135°C) draw rolls (16) , rotating at 2656 ypm. Following drawing, the heated filaments were crimped by a hot air, jet- bulking process (17) of the type described in Breen and Lauterbach, United States Patent 3,186,155. The bulking air temperature was 165°C. The hot fluid exhausted with the threadlines against a rotating drum (18) having a perforated surface, on which the yarns were cooled to set the crimp. From the drum (18) , the threadlines in bulky form passed to a pair of driven take-up rolls (19) onto rotating cores (20) and (20a) to form packages (21) and (21a). The percent void of the filaments was about 13%. Comparative Sample B Polypropylene filaments having cross-sections, as shown in Fig. 1-A, were made by the methods described for producing Sample A filaments, except that the melt- spinning dope was spun through a spinneret having the configuration shown in Fig. 1. Referring to Fig. 1, the outside diameter (F) of the spinneret capillary was 0.0791 inches. The width (G) of the peripheral spokes (22) was 0.0087 inches, while the width (H) of the radial spokes (23) was 0.0065 inches. The spacing (J) between the ends of the radial spokes was 0.0142 inches, while the spacing (K) between the ends of the peripheral spokes was 0.0060 inches. The depth of the capillary was 0.035 inches, and the length to diameter (L/D) ratio (0.035/0.0065) was about 5.4. The percent void of the filaments was about 12%. Yarn bundles composed of the above-described polypropylene filaments, Sample A and Comparative Sample B, were then inserted into respectively separate primary backings, and latex was applied. The yarns were inserted as loops to form commercial and residential level loop carpet samples. In the following Tables, those carpets comprising of yarn bundles made from Sample A filaments are identified as Sample A (Commercial) and A-l (Residential) carpets, and carpets comprising of yarn bundles made from Comparative Sample B filaments are identified as Comparative Sample B (Commercial) and B-l (Residential) carpets. Carpet Soiling Performance Test / Commercial Carpets The yarns comprising the commercial carpet samples had a draw finish at a level of .55%. The yarn bundles were single ended, with a base yarn of 2500 denier, and 120 filaments per yarn bundle. The carpet samples had a basis weight of 20 oz./yd2, with a pile height of .187 inches. No wet proces.sing was involved in the carpet construction in order to maintain a constant level of finish on the yarns. The commercial carpet samples (A and B) were tested for carpet soiling performance. Each sample was subjected to 491,000 foot traffics which represents the typical life span of a commercial carpet. Soiling ΔE measurements were taken at different intervals leading up to the 491,000 level. The results of the tests are shown in the following Table I. TABLE I (ΔE) TRAFFICS 70M* 139M 226M 296M 491M SAMPLE A 7.0 9.2 9.4 9.6 9.9 B (COMPARATIVE) 7.1 9.6 10.4 10.8 10.9 M* = thousand Carpet Soiling Performance Test/Residential Carpets The residential carpet Berber yarns were made by air entangling 6 ends of the above-described 2500 denier commercial yarns. The yarn bundles had a 15,000 denier, with 720 filaments per yarn bundle. The yarns had a draw finish at a level of .55%. These heavy denier yarns were tufted on a 1/4 gauge level loop machine at 40 oz./yd2. The pile height for the resulting carpets was .375 inches. The carpets had a primary backing with latex applied for dimensional stability, and no wet processing occurred during carpet construction, in order to maintain a constant level of finish on the yarns. The residential carpet samples (A-l and B-l) were floor tested for 340,000 foot traffics. (Residential applications do not require as many traffics as commercial applications.) The results of the tests are shown in the following Table II. TABLE II (ΔE ) TRAFFICS 83M* 115M 184M 340M SAMPLE A-l 5 . 3 8 . 0 8 . 9 10 . 0 B-l ( COMPARATIVE ) 7 . 1 8 . 9 10 . 8 12 . 2 M* = thousand Example 2 In this Example, polypropylene filaments were made by the two methods described in Example 1 and yarn bundles having a different base yarn denier were prepared. Sample C Polypropylene filaments having cross-sections, as shown in Fig. 2-A, were made by the method described for producing Sample A filaments. Comparative Sample D Polypropylene filaments having cross-sections, as shown in Fig. 1-A, were made by the method described for producing Comparative Sample B filaments. Carpet Soiling Performance Test/Commercial Carpets Yarn bundles composed of the above-described polypropylene filaments. Sample C and Comparative Sample D, were then inserted into respectively separate primary backings, and latex was applied. The yarns were inserted as loops to form commercial loop carpet samples. In the following Table III, carpets comprising of yarn bundles made from Sample C filaments are identified as Sample C and C-l carpets, and carpets comprising of yarn bundles made from Comparative Sample D filaments are identified as Comparative Sample D and D-l carpets. The yarn bundles had a base yarn of 1320 denier, with 70 filaments per bundle. The yarn bundles were made by air entangling either three ends of the base yarn (samples C and D) or four ends of the base yarn (samples C-l and D-l) . The carpet samples had a basis weight of 22 oz./yd2, with a pile height of .218 inches, and were tested for 352,000 traffics. The results are shown in Table III. TABLE III . (ΔE) TRAFFIC 157M* 352M SAMPLE C (3960 denier) 11.3 12.9 D (3960 denier) 12.4 13.9 C-l (5280 denier) 9.1 10.5 D-l (5280 denier) 10.4 11.3 Representative Example 3 The Filament Cross-Section Model was used in this Example. A measurement was taken to determine the soiling performance that a filament's cross-section could offer at different viewing angles. The first measurement was made on the flat surface, referred to as Oo viewing angle. A calculation was made, by dividing the visual distortion width by the total width. The visual distortion width and total width changed with each viewing angle. After the 0° measurement was taken, measurements were taken at 15°, 30° and 45° from the 0° angle. The 45° angle is the corner point of the filament's cross-section. These four angle measurements represented a spectrum of the filament's cross-section which continued to repeat around the surface of the 4 hole squares. The results are listed in Table IV. TABLE IV % SOILING PERFORMANCE VIEWING ANGLE Viewing Overall Angle 0° 15° 30° 45° Efficiency Sample E 57% 80% 97% 94% 84% F (Comparative) 38% 66% 89% 98% 74% Sample E - This sample represents the filaments of this invention, wherein each void is substantially centered on a side of the filament's cross-section. Sample F - This sample represents conventional filaments, wherein the voids are oriented at the corners of the filament's cross-section. Example 4 In this Example, nylon 66 filaments having cross- sections, similar to those shown in Fig. 4 with the primary difference being rounder shaped voids, were made by the following method. Nylon 66 polymer (polyhexamethylene adipamide) having a relative viscosity (RV) of about 41 was further polymerized to a higher RV of about 72 by a solid phase polymerization^process, melted at 288°C in a screw melter, and spun at 4.3 grams/hole/minute through a spinneret having the configuration shown in Fig. 2 and into a quench chimne . The spinneret had the following dimensions. The outside diameter (A) of the spinneret capillary was 0.0791 inches. The width (B) of the peripheral spokes (5) was 0.0080 inches, while the width (C) of the radial spokes (6) was 0.0065 inches. The spacing (D) between the ends of the radial spokes was 0.0100 inches, while the spacing (E) between the ends of the peripheral spokes was 0.0079 inches. The depth of the capillary was 0.035 inches, and the length to diameter (L/D) ratio (0.035/0.0065) was about 5.4. The quench air-flow rate was about 2.2 ft./sec and the temperature of the air was 10°C. The filaments were treated with aqueous liquid (a mixture of water and non- aqueous draw-finish material) , pulled by the feed roll which rotated at 858 ypm and drawn at 2.7 draw ratio by a pair of rolls heated at 205°C. Following drawing, the heated filaments were crimped with a hot air (230°C), jet- bulking process of the type described in Example 1. The denier per filament was about 19. The percent void of the filaments was about 9%. Yarn bundles composed of the above-described filaments were prepared. The yarn bundles were two ended with about 860 denier per end and 45 filaments per end (bundle) . Example 5 In this Example, nylon filaments having cross- sections, as shown in Fig. 4, were made by the following method. Nylon 66 polymer (polyhexamethylene adipamide) having a relative viscosity (RV) of about 41 was further polymerized to a higher RV of about 92 by a solid phase polymerization process, melted at 288°C in a screw melter, and spun at 4.3 grams/hole/minute through a spinneret having the configuration shown in Fig. 2 and into a quench chimney. The spinneret had the same dimensions of the spinneret in Example 4. The quench air flow rate was about 2.2 ft/sec and the temperature of the air was 10°C. The filaments were treated with aqueous liquid (a mixture of water and non- aqueous draw-finish material) , pulled by the feed roll which rotated at 858 ypm and drawn at 2.7 draw ratio by a pair of rolls heated at 205°C. Following drawing, the heated filaments were crimped with a hot air (230°C) , jet- bulking process of the type described in Example 1. The denier per filament was about 19. The percent void of the filaments was about 11%. Yarn bundles composed of the above-described filaments were prepared. The yarn bundles were two ended with about 860 denier per end and 45 filaments per end (bundle) . The relationship of relative viscosity (RV) to void content of the filaments is shown in Table V. TABLE V RELATIVE VISCOSITY/VOID CONTENT Example No. Relative Viscosity (RV) Percent Void 4 72 8.6% 5 92 11.1% Example 6 In this Example, polyester filaments having cross- sections, as shown in Fig. 5, were made by the following method. Polyethylene terephthalate polymer, with a relative viscosity measured in hexafluoroisopropanol (HRV) of 24, was melted at 281°C in a screw melter, fed through a filter pack, and spun through a spinneret having the configuration shown in Fig. 2 at a rate of 3.0 grams per minute per hole. The spinneret had the same dimensions of the spinneret in Example 4. The outside diameter of the spinneret capillary was 0.0791 inches. The width of the peripheral spokes was 0.0080 inches, while the width of the radial spokes was 0.0065 inches. The spacing between the ends of the radial spokes was 0.0100 inches, while the spacing between the ends of the peripheral spokes was 0.0079 inches. The depth of the capillary was 0.035 inches, and the length to diameter (L/D) ratio (0.035/0.0065) was about 5.4. There were 6 filaments per end. The extruded filaments passed through a chamber where they were cross- flow quenched with room temperature air and treated with aqueous liquid (a mixture of water and non-aqueous draw- finish material) . The yarn was pulled at a feed roll speed of 560 ypm and drawn at 2.5X draw ratio. The denier per filament was about 21. The percent void of the filaments was about 6%. Yarn bundles composed of the above-described filaments were prepared. Example 7 In this Example, polyester filaments having cross- sections, as shown in Fig. 6, were made by the following method. Polyethylene terephthalate polymer, with a relative viscosity measured in hexafluoroisopropanol (HRV) of 24, was melted at 281°C in a screw melter, fed through a .filter pack, and spun through a spinneret having the configuration shown in Fig. 2 at a rate of 3.0 grams per minute per hole. The spinneret had the same dimensions of the spinneret in Example 6, except for the outside diameter. The outside diameter of the spinneret capillary was 0.0120 inches. There were 6 filaments per end. The extruded filaments passed through a chamber, where they were cross- flow quenched with room temperature air and treated with aqueous liquid (a mixture of water and non-aqueous draw- finish material) . The yarn was pulled at a feed roll speed of 560 ypm and drawn at 2.5X draw ratio. The denier per filament was about 21. The percent void of the filaments was about 9%. Yarn bundles composed of the above-described filaments were prepared. Example 8 In this Example, nylon filaments having different cross-sections were prepared. Sample G Nylon filaments having cross-sections as shown in Fig. 7-A were prepared by the following method. Nylon 66 polymer was melted at 285°C in a screw melter and spun at 5.25 grams/hole/minute through a spinneret having the configuration shown in Fig. 7 and into a quench chimney. The RV of the polymer was 50 and the RV of the filament was 65. Referring to Fig. 7, the outside diameter (L) of the spinneret capillary was 0.0800 inches. The width (M) of the peripheral spokes was 0.0032 inches, while the width (N) of the radial spokes was 0.0024 inches. The length (0) of the radial spokes was 0.0110 inches. The width (P) of the inner spokes was 0.0030 inches, and the length (Q) of the inner spokes was 0.0650 inches. The depth of the capillary was 0.0150 inches. The quench air pressure was 6 mbar and the air temperature was 10.5°C. The filaments were treated with spin finish, pulled by a feed roll which rotated at 897 meters/minute and drawn at a 2.7 draw ratio by a pair of rolls heated at 205°C. Following drawing, the heated filaments were crimped in a hot air (236°C) jet-bulking process of the type described in Breen and Lauterbach, U.S. Patent 3,186,155. The bundle was 1350 dtex; each filament was 27 dtex. The percent void of the filaments was about 16%. Sample H (Comparative) Nylon filaments having cross-sections as shown in Fig. 8A, were made by the same method described for producing the filaments of Sample G, except that melted polymer was spun through a spinneret having the configuration shown in Fig. 8. Referring to Fig. 8, the outside diameter (R) of the spinneret capillary was 0.0800 inches. The width (S) of the peripheral spokes was 0.0031 inches, while the width (T) of the radial spokes was 0.0024 inches. The distance (u) between the peripheral spokes was 0.0080 inches, and the distance (V) between the radial spokes was 0.0150 inches. The capillary depth was 0.004 inches. The bundle was 1360 dtex; each filament was 30 dtex. The percent void was about 16%. Samples G and H were separately processed into 3 end intermingled yarns and tufted into standard 1/10 gauge level loop carpets and dyed. The carpet samples were tested for glitter. Carpets made from Sample G filaments of this invention had a glitter rating of 1.5 and had a pleasing wool-like appearance. Carpets made from comparative Sample H filaments had a glitter rating of 4. Example 9 Nylon filaments having the cross-section shown in Figure 9 were prepared by the following method. A nylon 66 random copolymer containing 3 percent by weight of the sodium salt of 5-sulfoisophthalic acid was melted at 290°C in a screw melter and spun at 4.38 grams/hole/minute through a spinneret having the configuration shown in Figure 7 and into a quench chimney. The RV of the polymer was 61. The spinneret dimensions were the same as those used in Example 8, Sample G, except that the length (0) of the radial spokes was 0.0120 inches and the length (Q) of the inner spokes was 0.0700 inches. The quench air flow rate was 2.2 feet/second and the quench air temperature was 10°C. The filaments were treated with spin finish, pulled by a feed roll which rotated at 949 yards/minute and drawn at a draw ratio of 2.7 by a pair of draw rolls heated at 184°C. Following drawing, the heated filaments were crimped in a hot air (220°C) jet-bulking process of the type described in Breen and Lauterbach, U.S. Patent No. 3,186,155. The bundle was 1235 denier; each filament was 19 dpf. ^ Soiling performance was satisfactory and glitter was comparable to that of Sample G in Example 8. The cross-sections of the filaments in this Example appear more square-shaped than do those in Sample G, Example 8. This is due to the difference in processing conditions, particularly the difference in polymer RV.

Claims: CLAIMS 1. A continuous filament, comprising a thermoplastic synthetic polymer and having a solid axial core and four substantially equispaced continuous nonround voids, a void content of about 6% to 25%, and a four sided cross-sectional contour, wherein each void is substantially centered on a side of the contour. 2. A continuous filament, comprising a thermoplastic synthetic polymer and having a solid axial core and four substantially equispaced continuous round voids, a void content of about 6% to 25%, and a four sided cross-sectional contour, wherein each void is substantially centered on a side of the contour. 3. A continuous filament, comprising a thermoplastic synthetic polymer and having a solid axial core and four substantially equispaced continuous triangular-like voids, a void content of about 6% to 25%, and a four sided cross-sectional contour, wherein the apex of each void is directed at the central longitudinal axis of the core, and the base of each void is substantially centered on a side of the contour. 4. The continuous filament of claim 1, 2, or 3, wherein the voids have substantially equal dimensions. 5. The continuous filament of claim 1, 2, or 3, wherein the polymer is selected from the group consisting of polyolefins, polyamides, and polyester. 6. The continuous filament of claim 5, wherein the polymer is polypropylene. 7. The continuous filament of claim 5, wherein the polymer is nylon 66. 8. The continuous filaments of claim 5, wherein the polymer is polyethylene terephthalate.

Inventors: LIN PERRY HAN-CHENG, LIN, PERRY, HAN-CHENG
Applicants: DU PONT, E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1994
Main classification: D01D5
IPC codes: D01D5